Dual-cylinder piston pump

ABSTRACT

The invention relates to a hydraulically actuated dual-cylinder piston pump ( 1 ), with a first differential cylinder ( 22 ), with a head-end chamber ( 51 ) and a rod-end chamber ( 53 ), which actuates a first delivery piston ( 4 ) via a first piston rod ( 6 ), and also with a second differential cylinder ( 23 ), with a head-end chamber ( 52 ) and a rod-end chamber ( 54 ), which actuates a second delivery piston ( 5 ) via a second piston rod ( 7 ), and with a switching device ( 14 ) which by switching the hydraulic oil flow to the chambers ( 51, 52,   53, 54 ) of the differential cylinders ( 22, 23 ) establishes a head-end or rod-end operating mode of the dual-cylinder piston pump ( 1 ), wherein the switching device ( 14 ) is arranged on the bottoms ( 48, 49 ) of the head-end chambers ( 51, 52 ) of the differential cylinders ( 22, 23 ) as a bridge-forming connection between the differential cylinders ( 22,   23 ). The invention is distinguished by the fact that the switching device ( 14 ) comprises through-passages ( 28, 29 ) for the hydraulic oil for actuating the differential cylinders ( 22,   23 ), via which the head-end chambers ( 51, 52 ) of the differential cylinders ( 22, 23 ) are connected to the switching device ( 14 ) without hydraulic oil lines. The object of the invention is also a method for operating a hydraulically actuated dual-cylinder piston pump according to the invention.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to International Patent Application No.PCT/EP2016/054779, filed Mar. 7, 2016, which claims the benefit of DEApplication No. 10 2015 103 180.9, filed Mar. 5, 2015, both of which areherein incorporated by reference in their entireties.

TECHNICAL FIELD

The invention relates to a dual-cylinder piston pump, for example forpumping thick substances, such as sludge or concrete, as are used forexample in automatic concrete pumps, stationary concrete pumps ortrailer concrete pumps.

BACKGROUND

A dual-cylinder piston pump, which is operated by hydraulic actuatingcylinders which as a rule are designed as differential cylinders, can beoperated in a head-end or in a rod-end operating mode. Whereas in thecase of the head-end operation the complete surfaces of the hydraulicpistons in the hydraulic cylinder are acted upon by hydraulic oil ineach case, in the case of the rod-end operation only a partial surfaceof the pistons is acted upon because in the case of the rod-endactuation the surface on which the piston rod is attached to thehydraulic piston is not effective for the hydraulic pressure. This leadsto the pump being operated with greater delivery volume but low deliverypressure in the case of the rod-end operation and being operated withhigher delivery pressure but smaller delivery volume in the case of thehead-end operation.

A changeover of the operating mode is advisable for example in the caseof stationary concrete pumps during construction of a building in whichat the beginning of the concrete delivery concrete is delivered with ahigher delivery quantity but low delivery pressure in stories located atlow level. With increasing construction progress, after reaching aspecified building height, a higher delivery pressure is necessary incertain circumstances in order to pump the concrete through the deliveryline to a corresponding building height, for which, however, a lowerconcrete output is accepted.

As a rule, the hydraulic actuation of dual-cylinder piston pumpsaccording to the prior art, as shown in FIG. 1, in which the head-endactuation is displayed, is constructed so that the hydraulic oil foractuating the differential cylinder 22, 23 of the dual-cylinder pistonpump 1 is directed via a control circuit (not shown) to the actuatingpiston 8 of a differential cylinder 22. Via a bridging oil line 13,which interconnects the two rod-end chambers 53, 54 of the differentialcylinders 22, 23, in the case of the head-end actuation of thedual-cylinder piston pump for example shown in FIG. 1, the hydraulic oilis forced from the rod-end chamber 53 of the first differential cylinder22 into the rod-end chamber 53 of the second differential cylinder 23and therefore the second hydraulic cylinder 23 is actuated. As soon asthe first delivery piston 4 reaches its end point, the hydraulic oil isdirected into the chamber 54 instead of into the chamber 53, as a resultof which the piston 9 of the second differential cylinder 23 is first ofall actuated and the hydraulic oil is directed via the bridging oil line13 from the rod-end chamber 54 of the second hydraulic cylinder 23 intothe rod-end chamber 53 of the first hydraulic cylinder 22.

It is basically possible, by modifying the hydraulic lines, to undertakethe changeover of head-end to rod-end operation of a dual-cylinderpiston pump, but this is very costly and in practice is hardly possibleat a building site since for example draining and replenishing of thehydraulic oil is required in order to alter the hydraulic hosearrangement.

A hydraulic circuit, which enables the switching between a rod-end andhead-side operating mode without modifying the hydraulic lines, is knownfrom document DE 292 56 74. Such a circuit, shown in principle in FIG.2, includes a switching block 14 which is connected via hydraulic lines15, 16, 17, 18 to the chambers of the differential cylinders 22, 23. Thearrows in FIG. 2 show the hydraulic oil flow in the head-end operatingmode of the dual-cylinder piston pump 1. Via a suitable switching devicein the switching block 14, the hydraulic oil flow is switched over sothat the dual-cylinder piston pump 1 is operated in rod-end mode.

In the case of such a switching device according to the prior art, adisadvantage is that leak tightness problems frequently occur on accountof the numerous connecting points for the hydraulic lines and highpressure losses occur on account of the numerous system components,which makes economical use of such hydraulic circuits difficult.Moreover, numerous hydraulic lines are required, which create a highinstallation and financial outlay and the complexity of the hosearrangement increases the risk of leaks.

In order to position the switching device 14 as close as possible to thehydraulic cylinders, this is attached to the hydraulic cylinders in themiddle, for example, as shown in FIG. 2. Since, however, the hydrauliccylinders can move relative to each other as a result of the high andvarying hydraulic pressures in the chambers, there is the danger thatcracks or other damage occur in the connecting point between thehydraulic cylinders and the switching device.

SUMMARY

The switching of the operating mode of a dual-cylinder piston pump,which could also be carried out automatically, is, however,safety-critical and should only be carried out if the operator is clearabout the altered operating conditions regarding the altered deliverypressure and the pumped delivery volume during the switching of theoperating mode.

It is therefore the object of the present invention to provide a simpledevice for switching between head-end and rod-end operating mode of adual-cylinder piston pump, and also to provide a method for theswitching of the operating mode, which resolve the aforesaiddisadvantages of the prior art.

These objects are achieved by means of a dual-cylinder piston pump, aswitching device, and methods according to the claims. Reference is tobe made to the fact that the features which are individually quoted inthe claims can also be combined with each other in an optional andtechnologically sensible manner and therefore demonstrate furtherembodiments of the invention.

A hydraulically actuated dual-cylinder piston pump according to theinvention comprises a first hydraulically operated differentialcylinder, with a head-end chamber and a rod-end chamber, which actuatesa first delivery piston via a first piston rod, a second differentialcylinder, with a head-end chamber and a rod-end chamber, which actuatesa second delivery piston via a second piston rod, and a switchingdevice, which by switching the hydraulic oil flow to the chambersestablishes a head-end or rod-end operating mode of the dual-cylinderpiston pump, wherein the switching device is arranged on the bottoms ofthe head-end chambers of the differential cylinders as a bridge-formingconnection between the differential cylinders. The invention isdistinguished by the fact that the switching device comprisesthrough-passages for the hydraulic oil for actuating the differentialcylinders, via which the head-end chambers of the differential cylindersare connected to the switching device without hydraulic oil lines.

Compared with the prior art, the dual-cylinder piston pump according tothe invention has the advantage that on the one hand a particularlyforce-locked connection of the components to each other is created sothat damage (e.g., crack developments, fractures) at or in the region ofthe connecting points between the differential cylinders and theswitching device is not to be taken into account. On the other hand, thedual-cylinder piston pump according to the invention, compared with theprior art, has the advantage that the risk of rupturing of hydraulichoses is greatly reduced since hydraulic hoses are required only betweenthe rod-end chambers of the differential cylinders and the switchingblock. Moreover, the cost for the installation and screw-connecting ofthe hydraulic hoses is greatly reduced.

In a preferred embodiment of the invention, the switching device isfastened on the bottoms of the differential cylinders with the aid ofadapter flanges. The particular advantage of this embodiment of theinvention exists in the fact that a modification of the switching deviceis dispensed with if the switching device is to be attached todifferential cylinders with different diameters because via the adapterflanges with different diameters, which are adapted in each case to theinside diameter of the head-end chamber of the differential cylinder,the switching device of the same type of construction can be adapted todifferential cylinders with different diameters. The adapter flanges canbe arranged in corresponding recesses in the switching block. Therecesses in the switching block increase the stability of thearrangement and at the same time unload the fastening/screwing of theadapter flanges.

The hydraulically actuated dual-cylinder piston pump can furthermorecomprise flanges arranged on the differential cylinders, by means ofwhich the differential cylinders are fastened, preferably screwed, tothe switching device. Such flanges enable a simple fastening/screwing ofthe differential cylinders to the switching device. The flanges are forexample attached to the tubular differential cylinders by means of awelded or screwed connection or already form a unit with the cylindertubes during production.

In a further preferred embodiment, the bottoms of the head-end chambersof the differential cylinders comprise close-fitting seats into whichthe adapter flanges are fitted. As a result of this measure, the adapterflanges absorb in an optimally form-locking manner the radial forceswhich originate from the differential cylinders and therefore avoid thetransverse force loading of the flange screws between the differentialcylinders and the control block. Moreover, the adapter flanges increasethe mechanical loadability/durability of the connection between thedifferential cylinders and the switching device.

In a further preferred embodiment of the invention, expansion sleevesare arranged on the flanges for accommodating screws. As a result ofthis, a secure screw fastening can be ensured between the flanges andthe switching device. As a result of the expansion sleeves, longerscrews can be used and the expansion sleeve absorbs some of theexpansion, e.g., as a result of thermal loads and pressure loads, in thematerial and therefore acts like a buffer, as a result of which the leaktightness of the cylinder chambers under high pressure is always ensuredand high safety standards are met.

A further preferred embodiment of the invention is distinguished by thefact that the switching device comprises an inlet for a control line forthe switching of the operating mode of the dual-cylinder piston pump.This control line can be for example hydraulically or electricallydesigned.

In a further preferred embodiment, the operating mode of thedual-cylinder piston pump is switched over via a pilot valve which isactuated via the control line. By means of a latching device, this pilotvalve is preferably also held in its last switched position in the eventof the control line being shut off or in the event of a signal to thecontrol line not being present, for example with the pump switched off.As a result of this, the effect of the pump being inadvertently startedin an operating mode with differs from the last used operating mode,e.g., during restarting, is prevented.

The invention is furthermore distinguished by a method which controlsthe changeover of the operating mode of the dual-cylinder piston pumpduring startup of the pump. A further method relates to the changeoverof the operating mode while the pumping process is running.

The invention and also the technical field are explained in more detailbelow with reference to the figures. Reference is to be made to the factthat the figures show a particularly preferred embodiment variant of theinvention. The invention, however, is not limited to the depictedembodiment variant. In particular, the invention, providing it istechnically sensible, covers any combinations of the technical featureswhich are quoted in the claims or are described in the description asbeing relevant to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 shows a dual-cylinder piston pump according to the prior artwithout a switching device for the operating mode,

FIG. 2 shows a dual-cylinder piston pump with a switching device for theoperating mode according to the prior art,

FIG. 3 shows a dual-cylinder piston pump according to the invention in ahead-end operating mode,

FIG. 4 shows a dual-cylinder piston pump according to the invention in arod-end operating mode,

FIG. 5 shows a perspective view of a switching device according to theinvention,

FIG. 6 shows a perspective view of a switching device with connecteddifferential cylinders according to the invention,

FIG. 7 shows a sectional view of the connection between the switchingblock and a differential cylinder according to the invention,

FIG. 8 shows a hydraulic circuit according to the invention,

FIG. 9 shows a flow diagram for a method according to the invention, and

FIG. 10 shows a flow diagram for a further method according to theinvention.

DETAILED DESCRIPTION

Shown in FIG. 1 and FIG. 2 are dual-cylinder piston pumps 1 according tothe prior art, as have already been explained further above. Thedual-cylinder piston pump 1 according to FIG. 1 comprises two deliverycylinders 2, 3 with delivery pistons 4, 5 which in each case areactuated via piston rods 6, 7 of differential cylinders 22, 23 withhydraulic pistons 8, 9. Arranged between the delivery cylinders 2, 3 andthe differential cylinders 22, 23 is a water tank 10 in which there iswater which flushes the delivery pistons 8, 9 on their rear side inorder to cool and to lubricate the pistons. Connected to the head-endchambers 51, 52 of the differential cylinders 22, 23 are hydraulicfeed/drain hoses 11, 12 via which the hydraulic oil for actuating thedifferential cylinders 22, 23 is fed from a hydraulic pump, which is notshown. The rod-end chambers 53, 54 are interconnected via a bridging oilline 13. A cylinder bottom 49, 50 is located in each case at the end ofthe head-end chambers 51, 52. The arrows in FIG. 1 show the flowdirection of the hydraulic oil for the head-end actuation of thedual-cylinder piston pump 1.

FIG. 2 shows a dual-cylinder piston pump 1 corresponding to FIG. 1,which is equipped with a switching device 14 for switching betweenrod-end and head-side operating mode. The switching device 14 as a ruleconsists of a solid metal block in which are introduced control valvesand through-passages for the hydraulic valves which are arranged in theswitching device 14 and is therefore also referred to as a control blockor switching block. The references switching block and switching device14 are used synonymously in the following text. The switching block 14includes a hydraulic circuit which is suitable for controlling thehydraulic oil flow to the cylinder chambers 51, 52, 53, 54 so that acorresponding operating mode can be established. The hydraulic oilfeed/drain lines 11, 12 are connected to the switching block 14. Thearrows show in FIG. 2 the flow direction of the hydraulic oil and themovement direction of the delivery pistons for a head-end operation ofthe dual-cylinder piston pump 1.

FIG. 3 shows an embodiment according to the invention of a dual-cylinderpiston pump 1 which comprises a first differential cylinder 22 with ahead-end chamber 51 and a rod-end chamber 53, wherein the differentialcylinder 22 actuates a first delivery piston 4 via a first piston rod 6.The dual-cylinder piston pump 1 also comprises a second differentialcylinder 23 with a head-end chamber 52 and a rod-end chamber 54, whichactuates a second delivery piston 5 via a second piston rod 7. Thedual-cylinder piston pump 1 also comprises a switching device 14 whichby switching the hydraulic oil flow to the chambers 51, 52, 53, 54 ofthe differential cylinders 22, 23 establishes a head-end or rod-endoperation of the dual-cylinder piston pump 1.

The switching device 14 is arranged on the bottoms 48, 49 of thehead-end chambers 51, 52 of the differential cylinders 22, 23 as abridge-forming between the differential cylinders 22, 23.

The switching block 14 comprises two through-passages 28, 29 (see alsoFIG. 6) via which the head-end chambers 51, 52 of the differentialcylinders 22, 23 are connected directly to the switching device 14. Viathe through-passages 28, 29, the hydraulic oil is directed directly fromthe switching device 14 to the head-end chambers 51, 52 of thedifferential cylinders 22, 23, as a result of which a failure-pronehydraulic hose arrangement according to the prior art between theswitching block 14 and the head-end chambers 51, 52 can be avoided.

Arranged between the switching device 14 and the bottoms 49, 50 of thedifferential cylinders 22, 23 are adapter flanges 20, 21 which enable anindividual adaptation of the switching block 14 to the differentialcylinders 22, 23 with different diameters.

The hydraulic oil flow represented by arrows in FIG. 3 shows thehead-end operating mode of the dual-cylinder piston pump 1. That is tosay, the hydraulic oil, which is conducted from a hydraulic pump, notshown, at high pressure via the hydraulic oil line 11 into the switchingblock 14, is directed from the switching block 14 into the head-endchamber 51 of the differential cylinder 22. In the chamber 51, thegreater volume in conjunction with the larger piston surface than in thecase of the rod-end actuation (see FIG. 4) creates the effect of thedelivery piston 4 being pushed to the left in the first deliverycylinder 2 with high force but comparatively slowly. The hydraulic oilin the rod-end chamber 53 is transported in the course of the movementvia the hydraulic line 16, the switching block 14 and the hydraulic line18 into the rod-end chamber 54 of the differential cylinder 23 andcreates the effect of the hydraulic piston 9 being pushed to the right.In the process, the hydraulic oil is drained from the head-end chamber52 of the differential cylinder 23 via the switching block 14 and thehydraulic line 12. The delivery cylinder 2 in FIG. 3 is in pump mode,whereas the delivery cylinder 3 is in suction mode.

As soon as the delivery pistons 4, 5 or the hydraulic pistons 8, 9 havereached their end position, which for example is detected by means ofsuitable limit switches or detectors, the hydraulic oil flow is switchedover and the hydraulic oil flows from the hydraulic pump through theline 12 into the switching block 14 and first all actuates the hydraulicpiston 9 via the head-end chamber. This mode, which is not shown, nowcreates the effect of the delivery cylinder 3 working in pumping mode,whereas the delivery cylinder 2 works in suction mode.

Shown in FIG. 4 is the dual-cylinder piston pump 1 from FIG. 3, in whichthe switching block 14 is changed over via the control line 19 from thehead-end operating mode into the rod-end operating mode of thedual-cylinder piston pump 1. That is to say, the hydraulic oil comingfrom the hydraulic feed line 11 in FIG. 4 is first of all conducted viathe switching block 14 into the rod-end chamber 53 of the differentialcylinder 22, as a result of which the delivery cylinder 2 with thedelivery piston 4 is in suction mode at comparatively high speed butwith lower force. In the process, the hydraulic oil from the head-endchamber 51 of the differential cylinder 22 is conducted via theswitching block 14 into the head-end chamber 52 of the differentialcylinder 23 and actuates the hydraulic piston 9 or the delivery piston 5in pumping mode. After switching of the hydraulic oil flow, the pumpingdirection of the delivery pistons of the dual-cylinder piston pump 1 isreversed, wherein the rod-end actuation is maintained providing theswitching block 14 is not switched over via the control line 19 into thehead-end operating mode.

FIG. 5 shows a perspective view of the switching block 14 according tothe invention with installed adapter flanges 20, 21 with thethrough-passages 28, 29. The adapter flanges 20, 21 are fitted incorresponding recesses in the switching block 14 and are preferablyscrewed to the switching block by means of six screws in each case. Theadapter flanges 20, 21 could also be screwed onto the switching block 14without the recesses in the switching block 14. The recesses in theswitching block 14 increase the stability of the arrangement and at thesame time unload the screw fastening of the adapter flanges 20, 21.Shown on the sides of the switching block 14 are inlet/outlet passages57 for the hydraulic lines. Arranged on the switching block 14 at thetop is the housing of a pilot valve 33 (see also FIG. 8) which by thecontrol line 19 is electronically acted upon by the control signal forthe establishing of the operating mode.

FIG. 6 shows the switching block 14 together with the differentialcylinders 22, 23 which via flanges 24, which are preferably connected tothe differential cylinders 22, 23 by means of welded connections 26, arefastened to, preferably screwed to, the switching block 14. The screwfastening of the flanges 24 to the switching block 14 is not shown inthis drawing, only the drilled holes 25 for the screw fastening arevisible. The flanges 24 can for example also be screwed to the cylindertubes or produced in one piece.

FIG. 7 shows in a perspective cross section the connection of thedifferential cylinder 22 via the adaptor flange 20 to the switchingblock 14. On the bottom 49 of the differential cylinder 22 provision ismade for a close-fitting seat 55 so that the adapter flange 20 is fittedinto the differential cylinder 22 in a form-fitting manner. Forleakage-free sealing between the adapter flange 20, the switching block14 and the differential cylinder 22, two sealing rings 30 are insertedin grooves in the adapter flange 20.

The adapter flange 20, on the side facing the switching block 14, has anoutside diameter dl which fits into a prepared cutout in the switchingblock 14. On the side facing the differential cylinder 22, the adapterflange 20 has the diameter d2 which is adapted to the inside diameter ofthe close-fitting seat 55 of the differential cylinder 22. The switchingblock 14 is preferably also provided with fits/close-fitting seats withthe diameter dl for accommodating the adapter flanges 20, 21 in therecesses provided for it. Arranged in the adapter flange 20, in themiddle, is a hole through which the hydraulic oil flows from the passage28 of the switching block 14 into the head-end chamber 51 of thedifferential cylinder 22. By using adapter flanges 20, 21 with differentdiameters d2, but identical diameters d1, the switching block 14together with the differential cylinders 22, 23 can be operated withdifferent diameters. In the case of concrete pumps, diameters of thedifferential cylinders of 20-25 cm, for example, are customary, whereinthe middle point of the differential cylinders in relation to each otheris often the same so that a switching block 14 of the same type ofconstruction can be connected to different differential cylinders 22,23.

The differential cylinder 22 is screwed via the welded-on flange 24 tothe switching block 14 by screws 27. The screwed connections haveexpansion sleeves 36 which increase the security of the screw fasteningeven under high pressure and extreme thermal loads because the hydraulicpressure in concrete pumps can be up to over 400 bar.

Shown in FIG. 8 is a possible hydraulic circuit, arranged in theswitching block 14, which is suitable for undertaking the switching ofthe operating mode of the dual-cylinder piston pump 1. The hydrauliccircuit mainly comprises six cartridge valves 41-46 which are controlledby an electromagnetically controlled pilot valve 33. Via the control oilinlet 35, which is protected by a check valve 34, hydraulic oil isconducted to the pilot valve 33 for controlling the cartridge valves41-46. Via the hydraulic oil inlet/outlets 47 and 48, the hydraulic oilwhich is required for operating the differential cylinders 22, 23 is fedto/drained from the switching block 14.

The cartridge valves 41-45 control the hydraulic oil flow to thehead-end/rod-end chambers of the differential cylinders in therespectively established operating mode. The cartridge valve 46 is ofslightly larger dimensions than the other cartridge valves 41-45. Thevalve 46 opens or closes the connection between the two head-endchambers 51, 52 of the differential cylinders 22, 23 via thethrough-passages 28, 29 which are shown schematically in FIG. 8.

The pilot valve 33 is set in FIG. 8 so that the cartridge valves 41, 45and 44 are closed via the control line 32 as a result of the control oilpressure and the cartridge valves 42, 43 and 46 are opened by springforce action. As a result of this valve setting, the rod-end operatingmode of the dual-cylinder piston pump 1 is established.

Via the electric control line 19, the pilot valve 33, by means of twosolenoids which are located at the side on the valve body, is reversedin a known manner. A mechanical latching device 56 ensures that thepilot valve 33 remains in the last established position even with thecontrol line 19 shut down (e.g. after a shutdown of the entire machine).

In the rod-end operating mode, as explained further above, the pistons8, 9 move more quickly than in the head-end operating mode, which is whythe hydraulic oil quantity to be passed through the cartridge valve 46between the head-end chambers is particularly large, which requires alarger dimensioning of this valve.

The hydraulic lines 16, 18 and also the hydraulic connections 47, 48 areshown as being doubled here because the quantity of hydraulic oil to bepassed through is of such magnitude that a simple hose arrangement withthicker hydraulic lines would not be feasible so that a parallel hosearrangement with thinner hydraulic lines is provided.

FIGS. 9 and 10 show flow diagrams for methods for controlling adual-cylinder piston pump 1, which relate to the switching processbetween the rod-end and the head-end operating mode.

In FIG. 9, startup of the pump 1 is requested by an operator in step100. Before the pump starts, the operating mode established during thelast operation of the pump 1, e.g., with reference to a memory input, isfirst of all determined in step 101. In step 102, the operator, forexample via a display on the control unit of the machine or on a remotecontrol unit, asks whether the pump is to be used again in the lastestablished operating mode, which is also displayed, during startup. Ifthe operating mode is to be maintained, via step 103 the pump is startedin this operating mode in step 105. If the operating mode is to bealtered, because the pump conditions have been altered (e.g., concretedelivery location at a higher or lower level during the restart), instep 104, by switching of the pilot valve 33, the operating mode isswitched over and only then is the pump started in step 105.

The sequence could also be configured so that in step 102 the operatorof the pump can acknowledge the maintaining of the operating mode in arelatively simple manner, whereas the switching of the operating moderequires a specific acknowledgement which expressly refers the operatorto the altered pump behavior. It is also conceivable that the operatingmode in step 102 is maintained after a certain waiting period (forexample 5 or 10 seconds) and the pump is automatically started in step105 if the operator makes no input within the waiting period.

FIG. 10 shows a method for switching the operating mode of the pump 1during continuous operation, in which the pressure of the pumped mediumor the hydraulic pressure of the hydraulic oil is measured at a suitablepoint, e.g., in one or both delivery cylinders 2, 3 in one or bothdifferential cylinders 22, 23 or in the switching block 14, in order toswitch the pump over into a suitable operating mode.

In step 110, the pump 1 is in normal pumping operation. At regularintervals, or even continuously, the pump pressure is checked in step111, and in step 113, based on the established operating mode 112, acheck is made as to whether the pump pressure lies within a tolerancerange for the operating mode. In the case of the rod-end actuation,which is better suited to speedier pumping at lower pressure, the pumppressure should not exceed for example a certain tolerance limit becausebeyond this limit the head-end operation is more suitable in certaincircumstances so as not to overload the hydraulic system. Since,however, various reasons can exist for the higher pump pressure, e.g.,even a blockage of the pipeline, the operator first of all asks in step114 whether the operating mode is to be maintained. If this is the case,the pump operation continues normally in step 110. If the change of theoperating mode is requested by the operator in step 115, the pilot valve33 is switched over and the pump operation is continued in step 117 withthe altered operating mode.

An automatic switching over from the head-end operating mode to therod-end operating mode (and vice versa) would also be conceivable if thepump pressure falls short of a certain tolerance limit in order toincrease the pump output. Since, however, the spontaneous change of theoperating mode at the building site can also bring problems along withit, a manual switching over with interrogation is to be preferred.Conversely, for example an automatic changeover to the head-endoperating mode could also be undesirable because the piping systemconnected to the pump is not designed for high pump pressure and pipesor hoses could burst.

LIST OF DESIGNATIONS

1 Dual-cylinder piston pump

2 First delivery cylinder

3 Second delivery cylinder

4 First delivery piston

5 Second delivery piston

6 First piston rod

7 Second piston rod

8 First hydraulic piston

9 Second hydraulic piston

10 Water tank

11 Hydraulic feed line

12 Hydraulic drain line

13 Bridging oil line

14 Switching device/switching block

15 First hydraulic line

16 Second hydraulic line

17 Third hydralic line

18 Fourth hydraulic line

19 Control line

20 First adapter flange

21 Second adapter flange

22 First differential cylinder

23 Second differential cylinder

24 Flange

25 Holes

26 Welded seam

27 Screws

28 Through-passage

29 Through-passage

30 Seals

31 First hydraulic control line

32 Second hydraulic control line

33 Pilot valve

34 Check valve

35 Connection for hydraulic control oil

36 Expansion sleeves

41-45 Cartridge valves for switching

46 Cartridge valve for connection of piston chambers

47 Hydraulic oil feed/drain

48 Hydraulic oil feed/drain

49 Bottom of differential cylinder 22

50 Bottom of differential cylinder 23

51 Head-end chamber of differential cylinder 22

52 Head-end chamber of differential cylinder 23

53 Rod-end chamber of differential cylinder 22

54 Rod-end chamber of differential cylinder 23

55 Close-fitting seat

56 Latching device for pilot valve

57 Inlet/outlet passages for the hydraulic lines

1. Hydraulically actuated dual-cylinder piston pump comprising: a firstdifferential cylinder, with a head-end chamber and a rod-end chamber,which actuates a first delivery piston via a first piston rod, a seconddifferential cylinder, with a head-end chamber and a rod-end chamber,which actuates a second delivery piston via a second piston rod, aswitching device which by switching the hydraulic oil flow to thechambers of the differential cylinders establishes a head-end or rod-endoperating mode of the dual-cylinder piston pump, wherein the switchingdevice is arranged on the bottoms of the head-end chambers of thedifferential cylinders as a bridge-forming connection between thedifferential cylinders, characterized in that the switching blockcomprises through-passages for the hydraulic oil for actuating thedifferential cylinders, via which the head-end chambers of thedifferential cylinders are connected to the switching device withouthydraulic oil lines.
 2. Hydraulically actuated dual-cylinder piston pumpaccording to claim 1, characterized by flanges, arranged on thedifferential cylinders, by means of which the differential cylinders arefastened, preferably screwed, to the switching device.
 3. Hydraulicallyactuated dual-cylinder piston pump according to claim 1, characterizedby-adapter flanges which are arranged between the switching device andthe bottoms of the differential cylinders.
 4. Hydraulically actuateddual-cylinder piston pump according to claim 3, characterized in thatthe adapter flanges are inserted into close-fitting seats which areintroduced into the bottoms of the differential cylinders. 5.Hydraulically actuated dual-cylinder piston pump according to claim 2,characterized in that the expansion sleeves are arranged on the flangesfor accommodating screws.
 6. Hydraulically actuated dual-cylinder pistonpump according to claim 1, characterized in that-the switching devicecomprises an inlet for a control line for the switching over of theoperating mode.
 7. Hydraulically actuated dual-cylinder piston pumpaccording to claim 6, characterized by a pilot valve for switching overthe operating mode of the switching device, which can be controlled bythe control line.
 8. Hydraulically actuated dual-cylinder piston pumpaccording to claim 7, characterized by a latching device which holds thepilot valve in its switched position when the control line is shut down.9. Switching device for establishing the operating mode of thehydraulically actuated dual-cylinder piston pump according to claim 1.10. Method for operating the hydraulically actuated dual-cylinder pistonpump according to claim 1, characterized in that before startup of thedual-cylinder piston pump the last established operating mode isdetermined a check is carried out as to whether the last establishedoperating mode is to be used for startup of the pump, and in that independence of this the operating mode is maintained or switched overbefore the pump is started.
 11. Method according to claim 10,characterized in that the last established operating mode is specifiedas the operating mode during startup of the pump.
 12. Method foroperating a hydraulically actuated dual-cylinder piston pump accordingto claim 1, characterized in that during the operation of thedual-cylinder piston pump the pump pressure is detected; it isdetermined whether the detected pump pressure lies within a specifiedtolerance for the established operating mode, and a check is carried outas to whether the operating mode is to be maintained, and in that independence of the result of the check the operating mode is maintainedor switched over.